Rotational positioning system in a wind turbine

ABSTRACT

A rotational positioning system in a wind turbine is provided that comprises a driven part, a plurality of positioning drives coupled to the driven part, a plurality of sensors each arranged to sense a load parameter indicative of the load of the respective positioning drive, and a load controller connected to the plurality of sensors. The load controller is arranged to determine a load of a respective positioning drive based on the sensed load parameter, to compare said load with an expected load value, and to output a signal indicative of a failure of the respective positioning drive in response to the load being smaller than the expected load value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation U.S. Pat. No. 9,869,298, filed Dec.28, 2012, which is a '371 of International Application NumberPCT/DK2011/050235, filed Jun. 24, 2011, which claims benefit of U.S.Provisional Application No. 61/359,576, filed Jun. 29, 2010 and claimspriority to Danish Application PA 2010 00565, filed Jun. 29, 2010. Eachof these applications is herein incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The invention relates to a rotational positioning system in a windturbine, and more particular to a rotational positioning system for thewind turbine yaw system.

DESCRIPTION OF THE RELATED ART

A wind turbine according to the state of the art is described in WO2009/068036 A2. For yaw control, the same comprises a yaw mechanism withone or more yaw motors, i.e. rotational positioning drives, and a yawbearing, which forms a rotatable connection between the wind turbinetower and the nacelle. The yaw motor or motors are cooperating with atoothed ring fixedly connected to the top of the tower, by a piniongear. Other wind turbine yawing systems are known from EP 1 571 334 A1or from WO 2008/053017 A3.

Further, it is known from DE 37 22 022 C1 to use a rotationalpositioning drive in a wind turbine, e.g. for pitch control of the rotorblades, wherein two separate motors are coupled to the element to bepositioned, i.e. the wind turbine blade, by means of a differentialgear. The motors are coupled to the differential gear by respective wormgears, the latter having self-inhibiting effects for the motors when notenergized.

In US 2003/160456 A1 an azimuth drive for wind energy plants, i.e. awind turbine yaw system, includes a plurality of three-phaseasynchronous motors, which are energized by a three-phase current ofvariable frequency and which are coupled in a negative feedbackrelationship by means of a current transformer for electricallystabilizing the individual motors from unwanted torque fluctuations inthe same.

SUMMARY OF THE INVENTION

According to a first aspect the invention provides for a rotationalpositioning system in a wind turbine. The rotational positioning systemcomprises a driven part, a plurality of positioning drives coupled tothe driven part, a plurality of sensors each arranged to sense a loadparameter indicative of the load of the respective positioning drive,and a load controller connected to the plurality of sensors. The loadcontroller is arranged to determine a load of a respective positioningdrive based on the sensed load parameter, to compare said load with anexpected load value, and to output a signal indicative of a failure ofthe respective positioning drive in response to the load being smallerthan the expected load value.

According to a second aspect the invention provides for a method ofrotationally positioning a driven part in a wind turbine. The drivenpart is driven by means of a plurality of positioning drives. A loadparameter indicative of the load of a respective positioning drive issensed. A load of a respective positioning drive is determined based onthe sensed load parameter. Said load is compared with an expected loadvalue. A signal indicative of a failure of the respective positioningdrive is outputted in response to the load being smaller than theexpected load value.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are explained by way of examplewith respect to the accompanying drawings, in which:

FIG. 1 illustrates a large modern wind turbine according to the state ofthe art, as seen from the front,

FIG. 2 shows a simplified cross-section of a wind turbine nacelle, asseen from the side,

FIG. 3 is a perspective view of a wind turbine yaw system, as known pese in the state of the art,

FIG. 4 is a simplified perspective view and schematic block diagram of awind turbine yaw system according to one embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is illustrating a large wind turbine, as indicated generally byreference numeral 1. The wind turbine 1 comprises a tapered tower 2 anda wind turbine nacelle 3, which is positioned on top of the tower 2. Awind turbine rotor 4 with a number of rotor blades 5, in the shownembodiment comprising three wind turbine blades 5, is connected to thenacelle 3 by means of a so-called low speed shaft, which is extendingout of the nacelle 3 front, at a rotor hub 14. The wind turbine nacelle3 is mounted on the top of the tower 2 to be able for azimuthal rotationaround a vertical axis, which is called “yawing”, so that the nacelle 3can follow the direction of wind or can be brought in a speciallydefined, feathered, position of the rotor blades 5 with reference to thewind direction under given circumstances. The wind turbine blades 5 arearranged such that the pitch of each blade 5, i.e. its inclination withrespect to the actual wind direction and speed can be adjusted orcontrolled. A pitch can be kept constant or can be varied during onerotation of the rotor 4, the latter for adapting to the wind speedvarying with the distance from the ground. Rotational positioningsystems are especially used for a wind turbine yaw control system tocontrol the yaw of the wind turbine nacelle 3 or for a wind turbinepitch control system to control the pitch of the wind turbine blades 5.

A wind turbine yaw control system, FIG. 3, as known per se in the art,comprises a plurality of yaw drives 102, each including a yaw motor 103and a yaw gear 104. Each of the yaw drives 102 should share the loadequally, or according to predefined proportions. Due to the extreme highyaw drive requirement, which has to be fulfilled by a proper yawingsystem to comply with any operating condition of the wind turbine, theyaw drives 102 are normally dimensioned in such way that any overloadrelay, that typically is included in the yaw system to protect the samefrom being damaged by excessive loads, under any normal conditions isnever closed to setting. This means that any failure of a yaw motor 103or, generally, the yaw drive 102 in the sense that the same does notcontribute to the yawing motion, is not detected. Typically, a yaw motor103 of a yaw drive is loaded not more than 50% during normal operation,thus motor failure might be not detected even if, theoretically, halfthe number of yaw motors is defective.

Before proceeding further with a detailed description of the embodimentsof the invention, some general aspects of the wind turbine positioningsystem shall be discussed.

In one embodiment, the rotational positioning system comprisespositioning drives that in turn each comprises one (or more) positioningmotor and a gear via which the positioning motor(s) is coupled to thedriven part. In another embodiment, the positioning drive comprises apositioning motor that is directly (without any intermediate gear)coupled to the driven part. The sensor are thus arranged to sense a loadparameter for the positioning motor or the gear, in both cases is theload parameter indicative of the load of the one (or more) positioningmotor. In general, the load parameter is sensed for any part of thepositioning drive that is subject to the torque transmission from thepositioning motor to the driven part provided that this load parameteris indicative of the load applied by the positioning motor. In anotherembodiment, two or more positioning motors are coupled together by onecommon gear, such as an differential gear, to the driven part.

In one embodiment the sensors for sensing the load parameter arearranged to sense a load parameter indicative of the effective motorpower, in particular an electric motor current, of the respectivepositioning motor.

Alternatively, or additionally, the sensors are arranged to sense a loadparameter indicative of the mechanical torque of the positioning drive.Again, the mechanical torque of the positioning drive may by sensed atany of its parts that is subject to the torque transmission from thepositioning motor to the driven part.

In one embodiment, the load controller is arranged to output a signalindicative of failure of the respective positioning drive in response tothe load being smaller by more than a predetermined amount than theexpected load value.

In one embodiment, the load controller is further arranged to output asignal indicative of failure of the respective positioning drive inresponse to the load being larger by more than a predetermined amountthan the expected load value. Thus, the controller outputs a failuresignal for a positioning drive that is not only working below normalload but that is also working a predetermined amount above normal load(such as in a jamming situation).

In one embodiment, the load controller is arranged to compare the loadof a respective positioning drive with the expected load value duringgiven operating intervals of the rotational positioning system, and tooutput a signal indicative of a failure of the positioning drive inresponse to the load being smaller or higher by a predetermined amountthan the expected load value during all or at least a part of the givenoperating intervals or during all or at least a part of each of thegiven operating intervals. The operating intervals may be chosen suchthat normal load distribution to the positioning drives is to beexpected during such an operating interval, such as excluding startingand braking intervals. Considering a plurality of such successiveoperating intervals, such as a number of successive rotational movementoperations of the rotational positioning system, minimizes the risk of amisdiagnosis of the failure of a positioning motor. The operatingintervals are relatively short, as those of a single positioningoperation, or they are longer, as hours, days or weeks, comprising alarge number of positioning operations.

In one embodiment, the rotational positioning system is arranged tocontrol the yaw of the wind turbine, in particular the pivotableconnection between a wind turbine tower and a wind turbine nacelle. Thedriven part is a yaw ring, and the positioning drive includes a yawmotor and a pinion meshing with the yaw ring. Again, some or allpositioning motors are grouped together into a plurality of motor groupsand each motor group is coupled via one gear, such as a differentialgear, to the yaw ring. Thereby, only a part or all of the positioningmotors of one motor group are equipped with the sensors for sensing theload parameter.

In another embodiment, the rotational positioning system is arranged tocontrol a pitch of the wind turbine blades.

Returning now to FIG. 1, according to one embodiment, the wind turbinerotor 4 comprises three rotor blades 5, which are mounted to the hub 14,but in other embodiments, the wind turbine rotor 4 might compriseanother number of blades 5, such as two, four or more blades.

FIG. 2 is showing a simplified cross-section of the nacelle 3 of aso-called pitch-regulated wind turbine 1, as seen from the side.Nacelles 3 may exist in a multitude of variations and configurations,e.g. a drive train in the nacelle 3, following the low speed shaft towhich the wind turbine rotor 4 is fixed, comprises one or more of thefollowing components: a gear 15 for changing the (low) rotational speedof the rotor 4 to an elevated rotational speed, some sort of brakesystem 16, and a generator 17 for converting the mechanical energyprovided from the wind turbine rotor 4 to electrical energy. Further,the nacelle 3 of a modern wind turbine 1 might also include a converter(or inverter) 18 for converting the electrical energy output from thegenerator 17 to a voltage with appropriate amplitude, frequency andphase for complying with the electrical grid requirements. Furtherincluded in the nacelle 3 might be additional peripheral equipment, suchas further power handling equipment, control equipment, hydraulicsystems, cooling systems and more.

The weight of the entire nacelle 3, including the nacelle components 15,16, 17, 18, is carried by a strengthening structure 19. The abovedescribed components 15, 16, 17, 18 may be placed on and/or connected tosuch a common load carrying structure 19. In the shown simplifiedembodiment, the strengthening structure 19 only extends along the bottomof the nacelle 3, e.g. in form of a bed frame, to which some or all thecomponents 15, 16, 17, 18 are connected. In other embodiments, thestrengthening structure 19 might comprise a so-called gear belltransferring the load from the rotor 4 directly to the tower 2, or theload carrying structure 19 might comprise several interconnected parts,such as in a lattice work.

In the shown embodiment, the drive train of the nacelle 3 is arranged inan angle relatively to a horizontal plane, e.g. for ensuring that therotor blades 5 do not hit the tower 2, for compensating for differencesin wind speed at the top and the bottom of the wind turbine rotor 4, andother reasons.

Most embodiments of modern wind turbines use so-called forced yawing,i.e. for controlling the direction or orientation of the nacelle 3 and,consequently, the axis of the wind turbine rotor 4, in the azimuthdirection around the vertical axis of the tower 2 and, consequently,relative to the wind direction, they make use of a yaw controllingsystem, which includes a controller 25 and a yaw system 24. The yawsystem 24 includes drives 102 to keep the rotor yawed against the windby rotating the nacelle 3 on the top of the tower 2.

The yaw system 24 shown in FIG. 2 comprises a yaw positioning drive 102which is cooperating with a toothed ring 101 by means of a pinion gear105, all those components illustrated in FIG. 2 in a very simplifiedmanner.

The yaw system is activated by the controller 25, which is, only for thepurpose of example, in the embodiment of FIG. 2, shown as included inthe rotor 4, for controlling the yaw angle or the yaw position, e.g. onthe basis of a position feedback signal from a position sensor. Insteadof being placed in the hub 14 of the rotor 4, in other embodiments, thecontroller 25 might be placed in the nacelle 3, in the tower 2, or atanother appropriate place.

The wind turbine blades 5 of the rotor 4 are connected to the hub 14pivotably around the longitudinal axis of the blades 5, i.e. in such away to enable variation of the blade pitch relatively to the wind. Thisincludes a feathered position, i.e. a parking position, where the blade5 is pitched so that the chord of the same is substantially parallelwith the incoming wind. For protective purposes, if the wind speed ofthe incoming wind increases above a certain level, such as e.g. 25meters/sec, the controller 25 will feather the blades 5 to make therotor 4 stop rotating, or at least make the rotor 4 idle, and the windturbine will substantially stop producing power to the utility grid.This is, among other reasons, for protecting the blades 5 and the othercomponents of the wind turbine 1 from damaging overloads at high windspeeds. The pitch control of the rotor blades 5 is performed by a pitchcontrol system or pitch positioning drives 21, 22, which in FIG. 2, forthe sake of simplicity and as an example only, are shown near the root29 of the blades 5.

FIG. 3 is showing, in a perspective, simplified view, some essentialparts of a wind turbine yaw system, as known per se from the state ofthe art. This comprises a yaw ring 101 and a plurality of yaw drives 102each including a yaw motor 103 and a yaw gear 104, wherein the yaw gear104 of each yaw drive 102 is coupled to the yaw ring 101 by a yaw pinion105, the latter meshing with the yaw ring 101. Such a yaw system,typically, is provided in the connection between the wind turbine tower2 and the wind turbine nacelle 3 of a wind turbine, as it is shown atreference numeral 24 in FIG. 2.

In FIG. 4, one embodiment of the inventive yaw system is shown in asimplified manner, partially in perspective view, partially in form of ablock diagram.

The yaw system comprises a yaw ring 101 and a plurality of yaw drives102 each including a yaw motor 103 and a yaw gear 104, wherein the yawgear 104 is coupled to the yaw ring 101 by a yaw pinion 105, the lattermeshing with the yaw ring 101. Whereas FIG. 3 shows a yaw system, inwhich the yaw drives 102 are arranged outside of the yaw ring 101, theyaw pinions 105 meshing with teeth of the yaw ring 101 on the outercircumference of the same, in FIG. 4 the yaw drives 102 are arrangedinside the yaw ring 101, the yaw pinion 105 meshing with teeth of theyaw ring 101 on the inner circumference of the same, only by the way ofan example. Further, FIG. 3 shows an arrangement including four yawdrives 102, whereas in FIG. 4, only for the sake of simplicity, thereare shown only three yaw drives 102.

Generally spoken, the yaw system includes a plurality of yaw motors 103within any kind of yaw drive 102 for driving the yaw system, and aplurality of sensors 111 for sensing a load parameter of a respectiveyaw motor 103 or, generally, the yaw drive 102. In FIG. 4, here areshown three yaw drives 102, each comprising one yaw motor 103 and oneyaw gear 104, the latter meshing with the yaw ring 101 of the yaw systemby one yaw pinion 105, each. In the present embodiment, each one ofthose yaw drives 102 has an associated sensor 111 for sensing the loadparameter.

The sensors 11 are coupled to a load controller, which is arranged toperform the following steps, for instance by the components 112, 113,114, 115 as shown in FIG. 4. In a first step (e.g. performed bycalculator 112) it determines a load of a respective yaw motor 103 basedon the load parameter sensed by the sensors 111. In a second step (e.g.performed by a comparator 113) it compares this load with an expectedload value. In a third step (e.g. performed by an outputting device 114)it outputs a signal 115 indicative of failure of the respective yawmotor in response to the load being smaller than the expected loadvalue. Such an expected load value may be based on the mean load valueof the plurality of yaw motors 103 of the yaw system, provided that theyaw motors 103 are similar or identical. In case that, for reasonswhatever, there are differences in the yaw drives 102 or yaw motors 103,as regards their power or load carrying ability, such differences aretaken in consideration when determining the mean load value.

The sensors 111 can be arranged to sense a load parameter, which isindicative of the effective power of the yaw motors 103, they can bearranged to sense an effective electric motor current of the yaw motors103 as the load parameter, or the sensors 111 can be arranged to sense amechanical torque of the yaw motors 103 or, generally, the yaw drives102 as the load parameter.

The load controller 112, 113, 114, 115 may further be arranged tocompare, based on the sensed load parameter, the load of the respectiveyaw motor 103 with the expected load value, and to additionally output asignal indicative of failure in response to the load being larger bymore than a given amount than the expected load value.

Additionally, or alternatively, the load controller 112, 113, 114, 115may be arranged to compare, based on the sensed load parameter, the loadof the respective yaw motor 103 or yaw drive 102 with the expected loadvalue during given operating intervals of the yaw system, and to outputthe signal indicative of failure, in response to the load being largerthan the expected load value during all or at least a part of all thegiven operating intervals or during all or at least a part of a each thegiven operating intervals.

Any significant deviation of the sensed load from the expected loadvalue, in the sense of being significantly smaller, but on the otherhand also when being significantly larger than the expected load value,may be considered as an indication of failure of one of the elements inthe yaw drive 102, be it in the yaw motor 103, the yaw gear 104, the yawpinion 105 or in any other essential part associated with the respectiveyaw drive 102. When the detected load, based on the sensed loadparameter, is significantly smaller than the expected load value, thiscan be considered as an indication of malfunction in the sense ofreduced driving performance, be it for whatever reason. On the otherhand, when the detected load, based on the sensed load parameter, issignificantly larger than the expected load value, this might, at arelatively early time, be considered as a malfunction in the sense ofany not normal, enhanced power requirement associated with the yaw drive102, may be by jamming or increased friction in the yaw motor 103, theyaw gear 104 or at another place.

Generally spoken, the sensed load of a respective yaw motor is comparedwith an expected load value in such way that the effective powerconsumption or load on each yaw motor is monitored, and if, on thisbasis, any failure of a yaw motor or yaw drive is detected, e.g. when amotor uses significantly less power than the others, the load controllerwill detect this, whereas the wind turbine is still able to continueproper operation.

The said comparison of the load, detected based on the sensed loadparameter, with the expected load value can be based on any appropriatereference value, this may be the mean load value of the plurality of theremaining yaw motors, the mean load value of all the yaw motors,including the respective one under consideration. The comparison,however, might also be done by deriving the expected load values fromthe operating parameters of the wind turbine, i.e. by modeling theexpected load value from parameters as wind direction, wind speed,rotational speed of the wind turbine, electric power output from thegenerator, and other operation parameters, or also by deriving theexpected load values from a look-up table to which the operatingparameters are input. However, the most appropriate way might be asimple comparison with the mean load or power requirement of the otheryaw motors.

LIST OF REFERENCE NUMERALS

-   1 wind turbine-   2 tower-   3 nacelle-   4 rotor-   5 blade-   14 hub-   15 gear-   16 breaking system-   17 generator-   18 converter-   19 strengthening structure-   21 pitch control system-   22 pitch control system-   24 yaw system-   25 yaw and pitch controller-   29 root-   101 yaw ring-   102 yaw drive-   103 yaw motor-   104 yaw gear-   105 yaw pinion-   111 load sensor-   112 load determining calculator-   113 load comparator-   114 failure signal outputting device-   115 failure signal

What is claimed is:
 1. A rotational positioning system in a windturbine, comprising: a driven part; a plurality of positioning drivescoupled to the driven part; a plurality of sensors each arranged tosense a load parameter indicative of a load of a respective positioningdrive; and a load controller connected to the plurality of sensors, andarranged to determine a load of the respective positioning drive basedon the sensed load parameter, to compare the load with an expected loadvalue, and to output a signal indicative of a failure of the respectivepositioning drive in response to the load being different from theexpected load value.
 2. The rotational positioning system of claim 1,wherein the load controller is arranged to determine the expected loadvalue as a mean load value of the plurality of positioning drives. 3.The rotational positioning system of claim 1, wherein the positioningdrives comprise positioning motors, and the sensors are arranged tosense a load parameter indicative of an effective motor power of a motorof the respective positioning drive.
 4. The rotational positioningsystem of claim 1, wherein the positioning drives comprise electricalpositioning motors, wherein the sensors are arranged to sense a loadparameter indicative of an electric motor current of the respectivepositioning motor.
 5. The rotational positioning system of claim 1,wherein the sensors are arranged to sense a load parameter indicative ofa mechanical torque of the respective positioning drive.
 6. Therotational positioning system of claim 1, wherein the load controller isarranged to output the signal indicative of the failure of therespective positioning drive in response to the load being different bymore than a predetermined amount than the expected load value.
 7. Therotational positioning system of claim 1, wherein the load controller isarranged to compare the load of the respective positioning drive withthe expected load value during given operating intervals of therotational positioning system, and to output the signal indicative ofthe failure of the respective positioning drive in response to the loadbeing different from the expected load value during all or at least apart of all of the given operating intervals or during all or at least apart of each of the given operating intervals.
 8. The rotationalpositioning system of claim 1, arranged to control yaw of the windturbine, wherein the driven part is a yaw ring, and the respectivepositioning drive comprises a yaw motor and a yaw pinion meshing withthe yaw ring.
 9. The rotational positioning system of claim 1, arrangedto control a pitch of wind turbine blades.
 10. A method of rotationallypositioning a driven part in a wind turbine, comprising: driving thedriven part by means of a plurality of positioning drives; sensing aload parameter indicative of a load of a respective positioning drive;determining the load of the respective positioning drive based on thesensed load parameter; comparing the load with an expected load value;and outputting a signal indicative of a failure of the respectivepositioning drive in response to the load being different from theexpected load value.
 11. The method of claim 10, further determining theexpected load value as a mean load of the plurality of positioningdrives.
 12. The method of claim 10, wherein sensing the load parametercomprises sensing a load parameter indicative of an effective motorpower of the respective positioning drive.
 13. The method of claim 12,wherein sensing the load parameter comprises sensing a load parameterindicative of an electric motor current of the respective positioningdrive.